FIGS. 14(A & B) illustrate a prior art surface acoustic wave (hereinafter referred to as SAW) resonator, which is an example of a piezoelectric device. FIG. 14(A) is a plan view of the SAW resonator with the lid 548 of FIG. 14(B) removed. FIG. 14(B) is a side sectional view taken along line M—M of FIG. 14(A). Piezoelectric devices are widely used for providing a constant frequency in electrical circuits. The SAW resonator 500 of FIG. 14(A), which illustrates the typical construction of a piezoelectric device, is manufactured by mounting a SAW resonating reed 510 in a package 540. Outer electrodes 552 disposed at the back side of the package 540 are electrically connected to interdigital transducer electrodes (hereinafter referred to as IDT electrodes) 512 disposed on the SAW resonating reed 510.
A pair of the IDT electrodes 512, which function as excitation electrodes to energize a surface acoustic wave resonator, is formed on the SAW resonating reed 510. Electrode pads 516 for the IDT electrodes 512 are also disposed on the SAW resonating reed 510 and are connected to the IDT electrodes 512. A package base 542 includes a cavity 544 for mounting the SAW resonating reed 510. The cavity 544 in the package base 542 preferably forms a stepped pattern along the sidewalls of the package base 542. A plurality of wire bonding pads 556 is formed on the middle step in the vicinity of electrode pads 516. The number of wire bonding pads 556 corresponds to that of the electrode pads 516 on the SAW resonating reed 510. Wiring patterns are formed on the package base 542 ranging from the wire bonding pads 556 to the outer electrodes 552. The electrode pads 516 are connected to the IDT electrodes and the wire bonding pads 556 by wires 550. Accordingly, the outer electrodes 552 of the package are electrically connected to the IDT electrodes 512 on the SAW resonating reed 510.
The SAW resonating reed 510 is mounted on the bottom of the cavity 544 of the package base 542 with an adhesive 538 such as a silver paste or a silicone resin paste. Furthermore, a lid 548 is installed at the opening of the cavity 544, thereby sealing the package 540 and keeping the SAW resonating reed 510 in an atmosphere such as nitrogen. Particles in the air are not deposited on the IDT electrodes 512, thereby preventing variation of the resonant frequency in the SAW resonator 500 over time.
FIGS. 15(A & B) illustrate a SAW filter, which is another example of a piezoelectric device of the prior art. FIG. 15(A) is a plan view of the SAW filter without a cover lid. FIG. 15(B) is a side sectional view taken along line P—P of FIG. 15(A). Two pairs of IDT excitation electrodes 612 and 613 may be formed on a SAW resonating reed 610 in a SAW filter 600. In yet other piezoelectric device(s), the excitation electrodes may be arranged in various patterns formed on the surface of the piezoelectric vibrating reed. The pattern of arrangement of the electrode pads for the excitation electrodes will vary accordingly. Wire bonding pads corresponding to the various types of electrode pads have to be formed on the package base. Unfortunately, to accommodate the different patterns various kinds of package base(s) are therefore required which makes a reduction in cost difficult to achieve.